1. Field of the Invention
The invention relates to control valves and particularly to sleeve valves in which the rate of fluid flow through the valve is dependent upon the rotational position of the sleeve with respect to the valve body.
2. Description of the Prior Art
Often in the control and utilization of fluids it is required to vary the flow rate of the fluid on one or both directions with a valve that is insertable directly within fluid line or circuit. The most common prior method for accomplishing fluid control was with the use of a needle valve which employed a tapered shaft valve needle the position of which was adjustable with respect to a valve seat. Such valves suffered from a number of disadvantages. To construct such a valve in which the position of the control needle was variable by rotation of an external sleeve was mechanically complicated, difficult to manufacture, and consequently somewhat expensive. The rate of flow as a function of control needle position with respect to the distance to the valve seat was nonlinear. The amount of control effected was disproportionately large for small amounts of needle position change so that a large increase or decrease in the rate of fluid flow through the valve was effected for small changes in needle position near valve closure. This effect was especially bothersome where high precision of control is required over a broad range of fluid flow rates.
Other prior art devices included one in which a metering disk was placed within the flow path of the fluid and the disk rotated at an angle to the direction of flow of the fluid to vary the rate of flow. Unfortunately, such devices suffered from many of the disadvantages of the previously described needle valve including the difficulty of attaining a precise control over the flow rate of fluids at small fluid flow rates and over a large range of fluid flow rates.
Devices were constructed with numerous differently shaped objects placed in the path of fluid control the position of which was movable to vary the rate at which fluid flowed through the valve by changing the cross-section of the aperture through which the fluid was restricted to pass. Many of the devices again suffered from the aforementioned problems attaining a fine degree of control over the flow rate of the fluid. Additionally, many were difficult to manufacture as exotically shaped aperture varying means were difficult to manufacture using standard machining techniques. Furthermore, in both needle and dish type valves, hysteresis problems caused the flow rate to be different depending upon whether the desired control position was approached from a higher or lower flow rate.